Statistical Tracing of Magnetic Fields: Comparing and Improving the Techniques

Yuen, Ka Ho; Chen, Junda; Hu, Yue; Ho, K.L.; Lazarían, A.; Lazarian, Victor; Yang, Bo; Burkhart, Blakesley; Correia, C.; Cho, Jungyeon; Canto, B.; Medeiros, J. R. De

doi:10.3847/1538-4357/aada88

Cited by 35 publications

(19 citation statements)

References 63 publications

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“…Lazarian et al (2017) claimed that for synchrotron intensities the latter can correctly trace mean magnetic field, but fails to trace the detailed magnetic field structure. A more detailed study using the velocity gradients and velocity anisotropies in Yuen et al (2018) confirmed this.…”

Section: Discussionmentioning

confidence: 53%

Tracing magnetic field with synchrotron polarization gradients: parameter study

Zhang

Lazarían

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We employ synthetic observations obtained with MHD simulations to study how to trace the distribution of turbulent magnetic fields using the synchrotron polarization gradient techniques suggested by . Both synchrotron polarization gradients and its derivative gradients with regard to the squared wavelength λ 2 are used to explore the probing ability of the technique in magnetic fields from sub-to super-Alfvénic turbulence. We focus on studies that involve multi-frequency measurements in the presence of strong Faraday rotation and show the ways of how to recover the projected mean magnetic fields in the plane of the sky and the local magnetic fields within a tomographic slice. We conclude that the new techniques can successfully reconstruct the 3D magnetic field within our Milky Way and other galaxies. This paper opens an avenue for applying our new techniques to a large number of data cubes such as those from the Low Frequency Array for Radio astronomy and the Square Kilometer Array.

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Section: Discussionmentioning

confidence: 53%

Tracing magnetic field with synchrotron polarization gradients: parameter study

Zhang

Lazarían

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…In the global reference frame, the anisotropy is dictated by the largest eddy (i.e., the eddy at scale l st for sub-Alfvénic turbulence) so that the observed anisotropy is scale-independent. However, due to the isotropic driving, it is possible to observe a (fake) scaledependent anisotropy in the global frame of reference, which is aligned with the mean magnetic field (see Vestuto et al 2003;Yuen et al 2018). This fake anisotropy comes from the isotropic driving.…”

Section: Structure Functions Of Turbulent Velocities In the Local And...mentioning

confidence: 99%

“…Consequently, the velocity centroid map and thin velocity channel can directly reveal velocity fluctuations in WIM and WNM. When the turbulent compression is significant, i.e., for supersonic CNM and molecular clouds (Zuckerman & Palmer 1974;Larson 1981;Chepurnov et al 2010), the situation is more complicated. Density fluctuations here are subjected to not only the Alfvénic mixing but also the shock compression.…”

Section: Application With 2d Velocity Informationmentioning

confidence: 99%

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Anisotropies in Compressible MHD Turbulence: Probing Magnetic Fields and Measuring Magnetization

Hu,

Xu,

Lazarian

2020

Preprint

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Probing magnetic fields in the interstellar medium (ISM) is notoriously challenging. Motivated by the modern theories of magnetohydrodynamic (MHD) turbulence and turbulence anisotropy, we introduce the Structure-Function Analysis (SFA) as a new approach to measure the magnetic field orientation and estimate the magnetization. We analyze the statistics of turbulent velocities in three-dimensional compressible MHD simulations through the second-order structure functions in both local and global reference frames. In the sub-Alfvénic turbulence with the magnetic energy larger than the turbulent energy, the SFA of turbulent velocities measured in the directions perpendicular and parallel to the magnetic field can be significantly different. Their ratio has a power-law dependence on the Alfvén Mach number M A , which is inversely proportional to the magnetic field strength. We demonstrate that the anisotropic structure functions of turbulent velocities can be used to estimate both the orientation and strength of magnetic fields. With turbulent velocities measured using different tracers, our approach can be generally applied to probing the magnetic fields in the multi-phase interstellar medium.

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“…Therefore, the POS magnetic field direction can be determined by varying the position angle from 0 to π. Note in numerical simulations, there exists a fake dependence of the anisotropy on length scales, due to the isotropic driving and insufficient inertial range (Cho & Vishniac 2000;Yuen et al 2018). To avoid this fake anisotropy, one should select R at sufficiently small scales away from the driving scale.…”

Section: Structure Function Analysismentioning

confidence: 99%

Anisotropic Turbulence in Position-Position-Velocity Space: Probing Three-Dimensional Magnetic Fields

Hu,

Lazarian,

2021

Preprint

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Direct measurements of three-dimensional magnetic fields in the interstellar medium (ISM) are not achievable. However, the anisotropic nature of magnetohydrodynamic (MHD) turbulence provides a novel way of tracing the magnetic fields. Guided by the advanced understanding of turbulence's anisotropy in the Position-Position-Velocity (PPV) space, we extend the Structure-Function Analysis (SFA) to measure both the three-dimensional magnetic field orientation and Alfvén Mach number M A , which provides the information on magnetic field strength. Following the theoretical framework developed in Kandel et al. ( 2016), we find that the anisotropy in a given velocity channel is affected by the inclination angle between the 3D magnetic field direction and the line-of-sight as well as media magnetization. We analyze the synthetic PPV cubes generated by incompressible and compressible MHD simulations. We confirm that the PPV channel's intensity fluctuations measured in various position angles reveal plane-of-the-sky magnetic field orientation. We show that by varying the channel width, the anisotropies of the intensity fluctuations in PPV space can be used to simultaneously estimate both magnetic field inclination angle and strength of total magnetic fields.

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Statistical Tracing of Magnetic Fields: Comparing and Improving the Techniques

Cited by 35 publications

References 63 publications

Tracing magnetic field with synchrotron polarization gradients: parameter study

Tracing magnetic field with synchrotron polarization gradients: parameter study

Anisotropies in Compressible MHD Turbulence: Probing Magnetic Fields and Measuring Magnetization

Anisotropic Turbulence in Position-Position-Velocity Space: Probing Three-Dimensional Magnetic Fields

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